U.S. patent application number 14/235388 was filed with the patent office on 2014-05-29 for voltage-limiting composition.
This patent application is currently assigned to SIEMENS AKTIENGESELLSCHAFT. The applicant listed for this patent is Peter Groppel, Steffen Lang. Invention is credited to Peter Groppel, Steffen Lang.
Application Number | 20140145123 14/235388 |
Document ID | / |
Family ID | 46551525 |
Filed Date | 2014-05-29 |
United States Patent
Application |
20140145123 |
Kind Code |
A1 |
Groppel; Peter ; et
al. |
May 29, 2014 |
VOLTAGE-LIMITING COMPOSITION
Abstract
A varistor, or voltage-limiting composition has a polymer matrix
and a particulate filler containing a partially conductive material
applied to an electrically non-conductive carrier material. The
carrier material has a lower density than the partially conductive
material, so that the settling rate of the filler in the polymer
matrix is reduced. The voltage-limiting composition can therefore
also be used as a lacquer or for prepreg materials. A body which
acts as a varistor may be produced using a composition of this kind
by a method that includes annealing. The varistor may be used for
surge arresters, in particular in medium-voltage systems,
low-voltage systems, cable connections and cable fasteners.
Inventors: |
Groppel; Peter; (Erlangen,
DE) ; Lang; Steffen; (Hallerndorf, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Groppel; Peter
Lang; Steffen |
Erlangen
Hallerndorf |
|
DE
DE |
|
|
Assignee: |
SIEMENS AKTIENGESELLSCHAFT
Munchen
DE
|
Family ID: |
46551525 |
Appl. No.: |
14/235388 |
Filed: |
July 13, 2012 |
PCT Filed: |
July 13, 2012 |
PCT NO: |
PCT/EP2012/063811 |
371 Date: |
January 27, 2014 |
Current U.S.
Class: |
252/519.33 |
Current CPC
Class: |
H01C 7/10 20130101; H01C
7/112 20130101; C08K 9/02 20130101; H01C 7/108 20130101 |
Class at
Publication: |
252/519.33 |
International
Class: |
H01C 7/10 20060101
H01C007/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 26, 2011 |
DE |
102011079813.7 |
Claims
1-14. (canceled)
15. A voltage-limiting composition, comprising: a polymer matrix;
and a particulate filler containing partially conductive material
applied to an electrically non-conductive carrier material that has
a lower density than the partially conductive material.
16. The composition as claimed in claim 15, wherein the partially
conductive material has at least one doped metal oxide.
17. The composition as claimed in claim 16, wherein the doped metal
oxide comprises doped tin oxide and/or doped zinc oxide.
18. The composition as claimed in claim 17, wherein the carrier
material has a density of less than 3.5 kg.m.sup.-3, in particular
of less than 3.0 kg.m.sup.-3.
19. The composition as claimed in claim 18, wherein the carrier
material consists of phyllosilicate.
20. The composition as claimed in claim 19, wherein the carrier
material is mica.
21. The composition as claimed in claim 20, wherein the carrier
material is a ceramic carrier material and the particulate filler
has been produced by annealing.
22. The composition as claimed in claim 21, wherein the polymer
matrix has an injection-moldable polymer.
23. The composition as claimed in claim 22, wherein the polymer
matrix has thermosetting and/or thermoplastic material.
24. A body, comprising: a voltage-limiting composition with a
polymer matrix and a particulate filler containing partially
conductive material applied to an electrically non-conductive
carrier material that has a lower density than the partially
conductive material.
25. The body as claimed in claim 24, wherein the body has at least
one layer of the voltage-limiting composition.
26. The body as claimed in claim 24, wherein the body has a basic
body produced from the voltage-limiting composition.
27. The body as claimed in claim 24, wherein the polymer matrix is
fiber-reinforced.
28. A method for producing a voltage-limiting composition from a
polymer matrix and a particulate filler containing partially
conductive material, comprising: annealing to produce the
particulate filler with the partially conductive material applied
to a lighter, electrically non-conducting carrier material.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is the U.S. national stage of International
Application No. PCT/EP2012/063811, filed, Jul. 13, 2012 and claims
the benefit thereof. The International Application claims the
benefit of German Application No. 10 2011 079 813.7 filed on Jul.
26, 2011, both applications are incorporated by reference herein in
their entirety.
BACKGROUND
[0002] Described below is a voltage-limiting composition, having a
polymer matrix and a particulate filler containing partially
conductive material. Also described is a body with such a
voltage-limiting composition and a method for producing a
voltage-limiting composition. The voltage-limiting composition can
be used particularly advantageously for surge arresters with a
varistor property, in particular in medium-voltage systems,
low-voltage systems, cable connections and cable fasteners.
[0003] Non-linear resistors with varistor behavior are used in a
wide variety of applications, such as in voltage protection
devices, in cable connections, in cable terminations, etc. These
non-linear resistors may contain a polymer matrix and a filler
embedded in the polymer matrix. The filler contains sintered
pellets with predominantly spherical particles of doped metal oxide
(metal-oxide varistor (MOV) filler). The particles of the pellets
have crystalline composite granular structures. Since a varistor
with a polymer matrix/MOV filler composite material can be produced
much more easily than a comparably acting varistor on the basis of
a sintered ceramic, varistors can be produced with the composite
material comparatively easily, inexpensively and in a great variety
of forms.
[0004] The viscosity of the composite material increases with
increasing filler content, until, depending on the matrix material
and the type of processing, a practical upper limit is reached, for
example of about 50 percent by weight in the case of casting
resins. In the case of lacquers and in the case of the production
of prepregs, the viscosity of the composite material is lowered by
adding solvent until ideal processability is achieved.
[0005] On account of the high density of doped metal oxides, of
typically more than 5 kg/m.sup.3, and the relatively low density of
the polymer of the polymer matrix, of about 0.8 to 1.3 kg/m.sup.3,
the filler quickly settles, as a result of which the maximum degree
of filling in the system is restricted, or makes a certain type of
processing virtually impossible. For instance, lacquers and
prepregs with a low viscosity and partially conductive fillers have
not so far been usable in practice.
[0006] WO 97/26693 describes such a polymer matrix/MOV filler
composite material. Powdered metal oxide pellets, which are
produced by sintering a spray-dried MOV powder on the basis of a
zinc oxide doped with oxides of Bi, Sb, Mn, Co, Al and/or further
metals is used as the filler. These pellets have spherical
particles formed like a soccer ball, with varistor behavior. The
particles have a diameter of up to 125 micrometers and vary in
their size with a Gaussian distribution. This material is used in
cable connections and cable terminations, where it forms
voltage-controlling layers.
SUMMARY
[0007] The voltage-limiting composition described below at least
partially overcomes the disadvantages of the related art and is a
voltage-limiting composition that can be processed better.
[0008] The voltage-limiting composition has a polymer matrix and a
particulate filler containing partially conductive material,
wherein the partially conductive material is applied to an
electrically non-conductive carrier material, and wherein the
carrier material has a lower density than the partially conductive
material.
[0009] The individual particles of the filler, which are therefore
made up partially of the less dense carrier material and partially
of the more dense partially conductive material, therefore have as
a whole a lower average density than the partially conductive
material, in particular metal oxide, alone, and consequently settle
to a lesser extent within the polymer matrix (improved settling
behavior). This allows the composition to be applied more uniformly
than before, with a higher filler content. The higher filler
content allows much higher current densities to be withstood before
the composition degrades. It is also now possible to provide a
composition for use as a lacquer and/or with prepregs that keeps a
sufficiently distributed high filler content over a sufficiently
long time for practical applications.
[0010] The polymer matrix may in particular be electrically
non-conducting or insulating, in particular after curing or the
like.
[0011] To provide the electrical partial conductivity (varistor
property), the particles of the filler of the voltage-limiting
composition may in particular form at least one conduction path
leading through the voltage-limiting composition, for which purpose
multiple particles come into mechanical and electrical contact, and
thus form electrically conductive clusters. With a low content of
conductive filler in a non-conductive matrix, such a conduction
path usually does not form, and a resistivity of the composition
will be almost infinitely high. With an increasing filler content,
the resistivity (in the conductive state of the filler) will fall,
until, as from what is known as a percolation limit or percolation
threshold, it is substantially constant (the composition is then
"percolation-saturated"). An increase of the filler content beyond
the percolation threshold will therefore no longer produce any
significant change in the resistivity and indicates a very strong
formation of electrical conduction paths or clusters in the matrix.
In the case of the present voltage-limiting composition (which is
therefore particularly percolation-saturated, i.e. has a filler
content at or beyond the percolation threshold), the percolation
threshold may be about 25 percent by weight to about 50 percent by
weight of filler. However, the voltage-limiting composition may
also have a filler content below the percolation threshold.
[0012] It is a development that the partially conductive material
is applied to an electrically non-conducting carrier material on
all sides. As a result, electrical contacting is ensured when there
is mechanical contacting, and formation of an electrical conduction
path is supported. Consequently, in this way a percolation
threshold can also be kept low.
[0013] The conductive material of the filler may in particular
include one or more compound semiconductors, in particular doped
compound semiconductors.
[0014] It is a refinement that the partially conductive material
has at least one doped metal oxide. Bi, Sb, Mn, Co, Al and/or other
metals, oxides thereof, or else fluorine (F) for example, may be
provided in particular as doping. Alternatively or in addition, the
partially conductive material may for example have III-IV compound
semiconductors, other II-VI compound semiconductors, Ill-VI
compound semiconductors, I-III-VI compound semiconductors, IV-IV
compound semiconductors (such as for example SiC), organic
semiconductors, etc.
[0015] It is also a refinement that the doped metal oxide includes
doped tin oxide and/or doped zinc oxide. These metal oxides have a
good voltage-limiting or varistor property. Tin oxide and zinc
oxide have comparatively high densities of about 6.9 kg.m.sup.-3
and about 5.6 kg.m.sup.-3, respectively.
[0016] It is also a refinement that the carrier material has a
density of less than 3.5 kg.m.sup.-3, in particular of less than
3.0 kg.m.sup.-3. Thus, a high difference in density in comparison
with the partially conductive material, in particular metal oxides,
can be ensured. Such carrier materials include, for example, boron
nitride, quartz, silicon carbide, silicon nitride or
phyllosilicates.
[0017] It is yet a further refinement that the carrier material is
a phyllosilicate. Apart from their low density, phyllosilicates, in
particular mica, have the advantage that they typically have only a
low electrical conductivity.
[0018] Mica especially has perfect basal cleavage and also has a
particularly low conductivity. Mica also has a particularly low
density of about 2.7 kg.m.sup.-3. The mica may for example be
muscovite or biotite. The phyllosilicates in particular, and among
them particularly mica, have the further advantage that, as small
particles, they have a flat basic form, for example even in the
form of powder. A small particle with a partially conductive
material applied to a phyllosilicate (in particular on all sides)
is consequently not spherical, but rather platelet-shaped. This
platelet form further slows down settling, since it opposes
movement in the polymer matrix with a higher flow resistance than a
spherical particle.
[0019] It is yet a further refinement that the carrier material is
a ceramic carrier material, for example mica. The ceramic carrier
material has the advantage that it is of high mechanical strength
and is chemically highly inert and, moreover, can be chosen as an
electrical insulator.
[0020] It is also a refinement that the particulate filler has been
produced by annealing, in particular with the ceramic carrier
material. The ceramic carrier material in this case has the
advantage that it is highly temperature-resistant and can withstand
the annealing undamaged.
[0021] It is a development that the particulate material, in
particular metal oxide, has been deposited as such or in a
preliminary form (for example in a not yet oxidized preliminary
form and/or with the addition of additives that are removed during
annealing) on the carrier material and then annealed with the
carrier material. The carrier material may for example be in the
form of a powder. Thus, firmly interconnected particles can be
produced, the ceramic carrier material having a temperature
resistance that is sufficiently high for annealing. For example,
the partially conductive material, in particular doped metal oxide,
may have been deposited as such or in the preliminary form on the
carrier material, in particular by a wet-chemical process. In
particular, for example, tin or zinc or a combination thereof
together with Bi, Sb, Mn, Co, Al etc. and possibly with additives
may be deposited wet-chemically on mica and be oxidized by the
annealing. The additives are thereby annealed out.
[0022] It is yet a further refinement that the polymer matrix has
an injection-moldable polymer. Thus, a voltage-limiting plastic
body, in particular solid body, with a varistor property can be
provided in an easy way by the composition.
[0023] It is yet another development that the composition is
flowable, for example as a result of adding solvent. The
composition can thus be used in particular as a lacquer or the like
with a varistor property.
[0024] It is also a refinement that the polymer matrix has
thermosetting and/or thermoplastic material. These polymers can be
used particularly well for producing plastic bodies, in particular
by an injection-molding process.
[0025] The individual particles of the particulate filler may in
particular have a predominant width of between 5 micrometers and 70
micrometers with a deviation (d95) from the predominant width of
+/-5 micrometers.
[0026] A thickness of the particles may in particular lie between
300 nanometers and 600 nanometers. In particular, a thickness of
the carrier may lie between 200 nanometers and 300 nanometers. The
doped metal oxide may have a thickness of in each case between 100
nanometers and 150 nanometers.
[0027] A body that has the voltage-limiting composition as
described above has the advantage that it fully or partially has
the voltage-limiting composition, which has a higher and/or more
uniformly distributed filler content of partially conductive
material, in particular of doped metal oxide, than known
voltage-limiting compositions. As a result, a more uniform varistor
behavior is made possible. Moreover, a body that can withstand much
higher current densities before degrading in its function as a
varistor is thus provided. This makes possible a varistor body that
is particularly durable with respect to current flow and is
operationally reliable.
[0028] It is a refinement that the body has at least one layer of
the voltage-limiting composition. Such a body has in particular the
advantage that its basic form, carrying the layer, can be produced
using a known process and then at least one layer of or with the
voltage-limiting composition can be applied. For the first time,
lacquers with the voltage-limiting composition may be used, because
the particles settle sufficiently slowly, and so the lacquer with a
high and sufficiently uniform filler content can be applied (for
example after previous shaking) by known methods (application by
brush, spraying on, etc.). In the case of lacquers, filler contents
of up to 90 percent by weight can be achieved with the
voltage-limiting composition.
[0029] It is another refinement that the body has or is a basic
body produced from the voltage-limiting composition. The body may
in particular only consist of the basic body. Thus, a particularly
durable and operationally reliable solid varistor body can also be
provided.
[0030] It is another refinement that the body has or is a
fiber-reinforced composition. In particular, the body may be in the
form of a semifinished prepreg or some other semifinished product
with a matrix of the composition and fibers for strengthening it.
It is therefore possible for the first time by use of the
voltage-limiting composition also to provide prepregs etc. with the
voltage-limiting competition, in particular with the
voltage-limiting composition as the matrix material of the prepreg.
In particular, fibers of the prepreg can thus be impregnated with a
voltage-limiting composition with a high and sufficiently uniform
filler content or be combined therewith. A prepreg may be
understood in particular as meaning a continuous fiber-reinforced
thermosetting semifinished product. However, the voltage-limiting
composition is not restricted to the use of continuous fibers, but
can for example also be used with thermosetting fiber-matrix
semifinished products, such as a BMC (Bulk Molding Compound) or SMC
(Sheet Molding Compound), which only have short fibers. The
thermosetting material of the prepreg or of another fiber-matrix
semifinished product may consequently be a voltage-limiting
composition with a thermosetting polymer matrix. For prepregs or
other fiber-matrix semifinished products, filler contents of up to
70 percent by weight can be achieved in the voltage-limiting
composition. However, the way in which it is formed is not
restricted to thermosetting materials.
[0031] A method for producing a voltage-limiting composition from a
polymer matrix and a particulate filler containing partially
conductive material includes annealing to produce the particulate
filler with the partially conductive material applied to a lighter,
electrically non-conducting, in particular ceramic, carrier
material. The method provides the same advantages as the
composition described above, and can also be of an analogous
form.
[0032] The properties, features and advantages of this
voltage-limiting composition are described above and the manner in
which they are achieved also becomes clearer and more easily
understandable in connection with the following schematic
description of exemplary embodiments, which are explained more
specifically in connection with the drawings. In these, elements
that are the same or act in the same way may be provided with the
same reference numerals for overall clarity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] These and other aspects and advantages will become more
apparent and more readily appreciated from the following
description of the exemplary embodiments, taken in conjunction with
the accompanying drawings of which:
[0034] FIG. 1 is a cross-section of a voltage-limiting
composition;
[0035] FIG. 2 is a cross-section of a body with a layer of the
voltage-limiting composition;
[0036] FIG. 3 is a cross-section of a body with a basic body
produced from the voltage-limiting composition; and
[0037] FIG. 4 is a cross-section of a body in the form of a prepreg
semifinished product with a fiber-reinforced voltage-limiting
composition.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0038] FIG. 1 shows a voltage-limiting composition 1. The
voltage-limiting composition 1 has an electrically non-conducting
polymer matrix 2 with one or more electrically non-conductive
thermosetting polymers. The polymer matrix 2 may also have further
materials or substances, for example solvents or thinners.
[0039] The polymer matrix 2 is mixed with a particulate filler,
which has powdered, partially conductive particles 4. This
voltage-limiting composition 1 acts as a varistor or has a varistor
function or varistor property, meaning that, up to a threshold
voltage applied thereto, the voltage-limiting composition 1 is
substantially electrically non-conducting and, when the threshold
voltage is reached or exceeded, it suddenly becomes substantially
conducting. The voltage-limiting composition 1 may therefore be
used for example for overvoltage protection.
[0040] The particles 4 are in the form of a composite material
("composite particles") such that a partially conductive material
in the form of a doped metal oxide 5 rests on a carrier or carrier
material 6 of mica, for example muscovite. Here, the doped metal
oxide 5 is a tin oxide or zinc oxide doped with an oxide of Bi, Sb,
Mn, Co and/or Al. While tin oxide and zinc oxide have a high
density of about 6.9 kg.m.sup.-3 and about 5.6 kg.m.sup.-3,
respectively, mica has a comparatively low density of about 2.7
kg.m.sup.-3. Mica is also decidedly electrically non-conducting.
The particles 4 therefore have an effective average density, which
is obtained from a weighted averaging of the densities of the doped
metal oxide 5 and the carrier 6 of mica. The particles 4 are
consequently lighter than pure doped metal oxide and sink to the
bottom considerably more slowly in the polymer matrix 2. The
carrier 6 therefore acts as a "float" for the metal oxide.
[0041] The sinking of the particles 4 is slowed down still further,
or even stopped, by the particles 4 not having a spherical form but
a platelet form, on account of the substantially planar carrier 6
of mica. The platelet form increases a flow resistance and thereby
reduces the sinking rate. Thus, even in a comparatively liquid
polymer matrix 2, the particles 4 can also be distributed
sufficiently long to make it possible for the voltage-limiting
composition 1 with a sufficiently high filler content to be
applied. The voltage-limiting composition 1 can consequently also
be used as a lacquer or a resin of a fiber-reinforced plastic.
[0042] The particles 4 may in particular have been produced such
that tin or zinc doped with Bi, Sb, Mn, Co and/or Al is deposited
wet-chemically on powdered mica and then annealed with the mica,
the oxides being formed during the annealing. The particles 4 may
in particular have a predominant width of between 5 micrometers and
15 micrometers, in particular between 7 micrometers and 9
micrometers. A thickness of the particles 4 may in particular lie
between 300 nanometers and 600 nanometers. In particular, a
thickness of the carrier or carrier material 6 may lie between 200
nanometers and 300 nanometers and the doped metal oxide 5 may be
present on both sides with a thickness of in each case between 100
nanometers and 150 nanometers.
[0043] Although the particles 4 are shown not touching one another
for the sake of good overall clarity, the voltage-limiting
composition 1 is in fact percolation-saturated, as diagrammatically
shown on an enlarged scale in detail A. Here the particles 4 are
arranged locally such that they are oriented substantially in the
same direction, and nearest neighbors of the particles 4 generally
touch (cluster formation). As a result, a very reliable form of
electrical conduction paths is made possible, and consequently a
reliable varistor function. For this purpose, the metal oxide 5
surrounds the carrier 6 in particular on all sides.
[0044] FIG. 2 shows a body K1 with a layer of the voltage-limiting
composition 1. The body K1 has a basic body 11 of an electrically
non-conducting material (for example plastic or ceramic), the basic
body 11 being covered on its surface with a layer 12 of the
voltage-limiting composition 1. If a voltage is applied to this
body K1, it acts as a non-conductor until the threshold voltage of
the doped metal oxide 5 is reached. When the threshold voltage is
reached or exceeded, the doped metal oxide 5 conducts. The body K1
consequently acts like a varistor. The voltage-limiting composition
1 may for example have been brushed or sprayed onto the basic body
11 as a lacquer. In this case, a weight content of the filler 4 may
be up to about 90 percent by weight.
[0045] FIG. 3 shows a body K2 with a basic body 13 produced from
the voltage-limiting composition 1. Here the basic body 13
therefore acts as a varistor. The voltage-limiting composition 1
may for example have been injection-molded to produce the basic
body 13. The polymer matrix 2 or the at least one associated
polymer is therefore likewise injection-moldable.
[0046] FIG. 4 shows a body in the form of a prepreg layer K3 with a
fiber-reinforced voltage-limiting composition 1. The associated
continuous fibers 14, impregnated with the voltage-limiting
composition 1, may be electrically conducting or electrically
non-conducting. Here, the prepreg layer K3 therefore acts as a
varistor or basic varistor material. The prepreg layer K3 may have
a weight content of the filler 4 of up to about 70 percent by
weight. Such a prepreg layer K3 may for example be or have been
wound around a basic body.
[0047] Although the voltage-limiting composition has been
illustrated more specifically and described in detail by the
exemplary embodiments shown, the voltage-limiting composition is
not restricted to these and other variations can be derived from
them by a person skilled in the art without departing from the
scope of protection of the invention.
[0048] A description has been provided with particular reference to
preferred embodiments thereof and examples, but it will be
understood that variations and modifications can be effected within
the spirit and scope of the claims which may include the phrase "at
least one of A, B and C" as an alternative expression that means
one or more of A, B and C may be used, contrary to the holding in
Superguide v. DIRECTV, 358 F3d 870, 69 USPQ2d 1865 (Fed. Cir.
2004).
* * * * *